1. Field of the Invention
The present invention relates to a dynamic pressure bearing device that utilizes a dynamic pressure of a lubricating fluid for supporting a shaft member by a bearing member.
2. Description of the Prior Art
In recent years, the development of a dynamic pressure bearing device has been pursued, which is a type of bearing for enabling a rotating member to rotate at high speed with high accuracy in various rotation driving devices. The dynamic pressure bearing uses a dynamic pressure of a lubricating fluid for supporting a rotating shaft. The dynamic pressure bearing device includes a dynamic pressure face of a shaft member and a dynamic pressure face of a bearing member, which are arranged to face each other and to be close in the radial direction or in the axial direction. Between the opposed dynamic pressure faces, a bearing space of a radial dynamic pressure bearing portion or a thrust dynamic pressure bearing portion is formed. An appropriate lubricating fluid is filled in the bearing space, and appropriate dynamic pressure generation means including a herringbone shaped groove generate a dynamic pressure in the lubricating fluid. The generated dynamic pressure is used for non-contact bearing of the shaft member by the bearing member in relatively rotatable manner.
In this dynamic pressure bearing device, the shaft member contacts with the bearing member temporarily at start or stop of rotation. Accordingly, a measure for improving abrasion resistance is provided to the dynamic pressure face of each member. For example, one of or both the dynamic pressure faces of the shaft member and the bearing member are provided with a sliding surface layer having abrasion resistance as described in Japanese unexamined patent publication No. 2001-289243. Such a sliding surface layer is made of a composite material including a thin metal plate as a substrate on which material containing zinc or tin is coated, a composite material coated with a solid lubricating material containing fluorocarbon resin, graphite or molybdenum disulfide, a ceramic such as alumina, or a copper type material such as aluminum bronze or manganese bronze. Furthermore, the above-mentioned thin metal plate is made of copper or a copper type material.
However, in this structure of the dynamic pressure bearing device including a sliding surface layer that has abrasion resistance to the dynamic pressure face of the shaft member or the bearing member, there is a case where the sliding surface layer comes off gradually from the surface after long period of usage. In this case, particles from the sliding surface layer will be suspended in the bearing space of the dynamic pressure bearing portion. If the suspended particles are caught between the shaft member and the bearing member, the dynamic pressure face may be damaged so that the dynamic pressure is lowered and a rotation locked state may happen.